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<megan@tpgi.com.au> writes:
Maybe Im losing the plot a little with this discussion on sensors and their
accuracy. Im a soil scientist involved with irrigation research as such I
have tried a number of devices escan, capacitance TDr neutron, tensiometers
gypsum. They work over different ranges and scales, but the biggest problem
is true calibration with the soil that they are installed in. The search
for the universal sensor that does not require calibration is over. We have
to get better with the gear we have which means doing the proper
calibrations every time we install one of these devices. On the other hand
I also try to promote the use of scheduling tools to growers. I can tell
you if it cant be used on every block on the farm or needs calibration or
is difficult to read you might as well forget about it. We need two sets of
gear one which is accurate so the scientist amongst us can get excited and
run around calibrating it the other something so simple and universal that
anyone can use it anywhere anytime....... the search continues.
On Friday, 7 May 1999 4:58, owner-sowacs@aqua.ccwr.ac.za
[SMTP:owner-sowacs@aqua.ccwr.ac.za] wrote:
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>
> "Peter Broomhall" <hortech@ats.com.au> writes
>
> >We see again and again, both on this list and related lists
> >(Irrigation/trickle) debate on accuracy etc of various soil moisture
> >sensors. A lot of the time....
> >>>>>>>>>>>>>>>>>>>>>
> I appreciate Peter Broomhall's directness. Too often the focus does
> seem to be on the sensor and not the interpretation of the data. Fact
> remains, for
> anybody to claim expertise in soil moisture feedback system design and
> operation for irrigation schedulers, they'd better know the various
> sensor's limitations
> and sensitivity to spacial variation. What attributes establish the
> value of a sensor?
> Cost to deploy, obviously, and perhaps the following:
> 1) Return to field capacity reading (highest repeatability over time
> and conditions on a scale of 1-10)
> factored by the
> 2) Volume of soil considered ("sphere of interrogation" on a scale
> of 1-10)
> might yield an indicator
> of "Dollars per unit of Reliability". The objective is to derive as
> much reliable i.e. volume
> information as possible for the least cost. After all, sensors aren't
> the key. The sufficiently compensated experts to interprete the data
> are the key.
>
> The quest to manage water resources better, to return higher profits
>
> to growers, while conserving water and fuel resources for future
> generations, all the while minimizing irrigation pump-related air
> pollution depends on expert interpretation of robustly constructed ,
> expertly
> installed sensors and data acquisition links. I wish there was more
> sponsorship of
> "demonstration" centers to show the comparativeness of different
> sensors,
> under differing deployment schemes. All the recent interest is great.
> A recently
> published quarterly newletter shows calculations and assumptions for
> determining
> number of sensors based on std. deviation and square root of mean..
> It begs the question, Why aren't the sensors configured to sample a
> larger
> volume to start with?
>
> Tom Reynolds
> Water Balance
> Mesa, AZ
>
>
>